Combustible Gas contamination in Hot Oil systems - The flash/fire point gap
Q: A client recently submitted an oil sample for flash and fire point testing. The system being sampled was for heat transfer. The flash and fire point (Cleveland Open Cup ASTM D92) were about 110°F apart from each other. This is surprising- what could be the reason for this?
A: It is certainly unusual to see such a wide temperature range between flash and fire point - a range of 20 to 40° F is more common. First let’s define flash and fire points: Flash point is the lowest temperature at which the vapor of a combustible liquid can be made to ignite momentarily in air. Fire point is defined as the temperature at which the vapor of a combustible liquid is sufficient to sustain combustion. A wide variation as observed can indicate the oil is contaminated. A possible contaminant exhibiting this phenomenon would be a combustible gas such as propane. As the oil is heated up to perform the flash point test, the gas comes out of the oil as vapor, which can momentarily ignite, thus determining the flash point. As the oil continues to heat up the combustible gas vapor is driven off, and the fire point is predominantly the property of the oil.
-Marc Jean
